(1) Field of the Invention
The present invention relates to the stabilization of hypochlorite-containing liquid laundry detergents which contain optical brighteners.
Sodium hypochlorite is known as a highly effective bleaching agent and has long been used, optionally together with soaps and/or synthetic surfactants, for removing stains and all kinds of soiling, not only when laundering textiles but also when cleaning hard surfaces. It is usually sold for household use in concentrations of approx. 2 wt. % to 10 wt. % in water.
Liquid laundry detergent preparations or corresponding preparations of cleaning agents for hard surfaces which contain hypochlorite as bleaching component are susceptible, when stored for an extended period, to suffering a loss in activity, in particular, due to the hypochlorite degradation which occurs in such cases. Constituents which are desired in laundry detergents and cleaning agents from an applicational standpoint or for aesthetic reasons also include, in addition to the active ingredients which decisively influence performance, among which hypochlorite may, in particular, be mentioned, those active ingredients which tend more to have an impact on the optical appearance of the textiles treated therewith. These, in particular, include optical brighteners which become attached to the fibers of the textile material during the washing operation. These compounds are capable of absorbing light and emitting shorter wavelength light. The overall result of absorbing red and yellow colored light and emitting blue to ultraviolet light is an increase in the intensity of light perceived as white, such that a textile treated in this manner appears optically brighter. For white laundry, this is a very desirable effect; laundry detergents which are intended to be used for washing colored textiles generally contain no optical brighteners. Optical brighteners are highly susceptible to oxidative attack by hypochlorite, which means that, after storage, corresponding agents containing both of these components, in addition to the consequent loss of bleaching agent, also exhibit the disadvantage that the active ingredient of the optical brightener which is jointly responsible for the optical impression of whiteness is no longer available, or at least not in its entirety.
(2) Description of Related Art, Including Information Disclosed Under 37 C.F.R. Sections 1.97 and 1.98
International Patent Application WO 99/15616 proposes adding free-radical scavengers to hypohalite-containing bleaching agents which contain optical brighteners in order to stabilize the optical brighteners.